Effects of Vegetarian or Vegan Diets on Glycemic and Cardiometabolic Health in Type 2 Diabetes: A Systematic Review and Meta-analysis

CONTEXT: Uncertainties still exist about the effect of vegetarian or vegan diets on glycemic and cardiometabolic risk factors in individuals with type 2 diabetes mellitus (T2DM), although plant-based diets are thought to be beneficial for cardiometabolic health. OBJECTIVE: The aim was to investigate whether vegetarian or vegan diets can improve blood glucose and cardiometabolic health in patients with T2DM compared with omnivorous diets. DATA SOURCES: Five databases (PubMed, Web of Science, Cochrane Library, Scopus, and Embase) were searched for eligible randomized controlled trials (RCTs) up to May 24, 2024. DATA EXTRACTION: Two authors independently performed the data extraction and quality assessment. DATA ANALYSIS: Nine RCTs (681 participants) were included in this meta-analysis. The results indicated that vegetarian or vegan diets could reduce glycosylated hemoglobin, type A1C (HbA1c) (weighted mean difference [WMD] = -0.36%; 95% CI: -0.54, -0.19; P < .001), low-density-lipoprotein cholesterol (WMD = -0.16 mmol/L; 95% CI: -0.26, -0.07; P = .001, and body mass index (WMD = -0.94 kg/m2; 95% CI: -1.43, -0.45; P = .0002) in a population with T2DM; however, they resulted in no significant improvement in systolic blood pressure and fasting plasma glucose. In subgroup analyses, the positive effects of a vegan diet were superior to a vegetarian diet for cardiometabolic health. HbA1c was reduced when vegetarian or vegan intake was more than 12 weeks. CONCLUSION: In conclusion, vegetarian or vegan diets could be utilized as a synergistic intervention in the T2DM population, contributing to cardiovascular disease prevention. In the future, the proportion of components that make up a plant-based diet should be explored. SYSTEMATIC REVIEW REGISTRATION: PROSPERO registration no. CRD42024578613.